Phosphors that emit visible light (typically, light with a wavelength of 380 nm or more to less than 830 nm) upon ultraviolet irradiation are used, for example, in display devices, such as lighting systems, televisions, and plasma displays, electronic microscopes, X-ray photography, signs, photovoltaic devices, and biology experiments. For the phosphors, materials containing rare earth elements as light-emitting elements have often been used (e.g., Patent Literature 1 to 3). However, rare earth elements are disadvantageous in that the reserves are small, the countries of production are limited, and the costs for separation and purification are high. Thus, there has been demand for phosphors containing an element other than a rare earth element as a light-emitting element.
Of the phosphors containing an element other than a rare earth element as a light-emitting element, red phosphor 3.6 MgO.4CaF2—GeO2:0.01 Mn containing Mn4+ as a light-emitting element is known as an oxide-based material with excellent stability (e.g., Patent Literature 4). Another oxide-based material known as having excellent stability is green phosphor ZnGa2O4:Mn containing Mn2+ as a light-emitting element (e.g., Patent Literature 5). ZnO having an oxygen defect as a luminescence center is known (e.g., Patent Literature 6) as a green or blue phosphor. Moreover, faujasite zeolites containing Ag ions are known to become phosphors ranging from orange to green (e.g., Patent Literature 7).
It has been reported that phosphors obtained by adding titanium to a high-purity zirconium oxide exhibit bluish white fluorescence under excitation of ultraviolet light (Non-Patent Literature 1 to 3).
However, there have been few studies on attempts to achieve fluorescence by adding a small amount of an element other than a rare earth element to zirconium oxide, and high fluorescence characteristics have yet to be achieved.